JP3567708B2 - Exhaust gas purification catalyst - Google Patents

Description

【００４９】
【表２】

【００５０】
表２より、実施例の触媒は変化率が５０％未満と小さく、高温熱処理によってもＮＯ_ｘ 吸蔵能の低下度合いが小さいのに対し、比較例の触媒では変化率が６９％以上と大きく、熱処理によってＮＯ_ｘ 吸蔵能が大きく低下している。すなわち実施例の触媒は比較例の触媒に比べて熱処理後にもＮＯ_ｘ 吸蔵体の硫黄被毒が抑制されていることが明らかである。
【００５１】
また実施例どうしを比較すると、ＷＯ_３ 又はＭｏＯ_３の量が３０重量％である実施例５及び実施例１３の触媒は、他の実施例に比べてＮＯ_ｘ 吸蔵量の絶対量が少ないことから、ＷＯ_３ 又はＭｏＯ_３は２５重量％以下とすることが特に望ましいことも明らかである。
このように実施例の触媒が比較例に比べて熱処理後にも硫黄被毒が抑制される理由は明らかではないが、実施例の触媒は比較例の触媒に比べて高温熱処理による担体の酸性質の低下度合いが小さく、担体の耐熱性が高いことに起因すると考えられる。
【００５２】
（実施例１８）
タングステン酸アンモニウム２０．３ｇをシュウ酸水溶液に溶解し、そこに水酸化ジルコニウム１１０．０ ｇを混合して１時間攪拌した後、水分を蒸発乾固により除去した。続いて１２０ ℃の乾燥炉で乾燥し、大気中にて８００ ℃で３時間焼成した。
得られたＷＯ_３／ＺｒＯ_２粉末をγ−Ａｌ_２Ｏ_３粉末と重量比で１：１で混合し、その混合粉末に所定濃度のジニトロジアンミン白金水溶液の所定量を含浸させ、大気中にて２５０ ℃で１時間焼成した。さらに所定濃度の酢酸カリウム水溶液の所定量を含浸させ、蒸発乾固後、大気中にて５００ ℃で１時間焼成して、実施例１８の触媒粉末を得た。Ｐｔの担持量は１重量％であり、Ｋの担持量は６重量％である。
【００５３】
（実施例１９）
実施例１８と同様にして得られた混合粉末にＰｔを担持した後、所定濃度の酢酸カリウム水溶液の所定量を含浸させ、蒸発乾固後、大気中にて２５０ ℃で１時間焼成した。この粉末にさらに所定所定濃度の酢酸バリウム水溶液の所定量を含浸させ、蒸発乾固後、大気中にて５００ ℃で１時間焼成して実施例１９の触媒粉末を調製した。Ｐｔの担持量は１重量％であり、Ｋの担持量は３重量％、Ｂａの担持量は９重量％である。
【００５４】
（実施例２０〜２５）
実施例１８と同様にして得られたＷＯ_３／ＺｒＯ_２粉末とγ−Ａｌ_２Ｏ_３粉末との混合比を、表３に示すように変化させたこと以外は実施例１８と同様にして、各実施例の触媒粉末をそれぞれ調製した。それぞれの触媒粉末のＰｔの担持量は１重量％であり、Ｋの担持量は６重量％である。
【００５５】
（実施例２６）
モリブデン酸１３．０ｇをシュウ酸水溶液に溶解し、そこに水酸化ジルコニウム１４１．２ ｇを混合して１時間攪拌した後、水分を蒸発乾固により除去した。続いて１２０ ℃の乾燥炉で乾燥し、大気中にて８００ ℃で３時間焼成した。
得られたＭｏＯ_３／ＺｒＯ_２ 粉末をγ−Ａｌ_２Ｏ_３粉末と重量比で１：１で混合し、その混合粉末に所定濃度のジニトロジアンミン白金水溶液の所定量を含浸させ、大気中にて２５０ ℃で１時間焼成した。さらに所定濃度の酢酸カリウム水溶液の所定量を含浸させ、蒸発乾固後、大気中にて５００ ℃で１時間焼成して、実施例２６の触媒粉末を得た。Ｐｔの担持量は１重量％であり、Ｋの担持量は６重量％である。
【００５６】
（比較例７）
ＴｉＯ_２粉末をγ−Ａｌ_２Ｏ_３粉末と重量比で１：１で混合し、その混合粉末に所定濃度のジニトロジアンミン白金水溶液の所定量を含浸させ、大気中にて２５０ ℃で１時間焼成した。さらに所定濃度の酢酸カリウム水溶液の所定量を含浸させ、蒸発乾固後、大気中にて５００ ℃で１時間焼成して、比較例７の触媒粉末を得た。Ｐｔの担持量は１重量％であり、Ｋの担持量は６重量％である。
【００５７】
（試験・評価）
それぞれの触媒粉末を １．０〜１．７ ｍｍのペレットに造粒し、それぞれのペレット触媒とした。このペレット触媒をそれぞれ評価装置内に配置し、空燃比Ａ／Ｆ＝１２相当のリッチモデルガス（表１のモデルガスＢ）とＡ／Ｆ＝２１相当のリーンモデルガス（表１のモデルガスＣ）を１分／４分の時間で切り替えながら、入りガス温度７００ ℃で５時間流通させる耐久試験を行った。
【００５８】
耐久試験後の実施例１８と比較例７の触媒粉末を、室温から ７００℃まで速度 ℃／分で昇温し、ＳＯ_２ の脱離量を測定した。結果を図１に示す。
また耐久試験後のそれぞれのペレット触媒について、硫黄の残留量を測定するとともに、表１のモデルガスＤを用い、入りガス温度３００ ℃、空間速度ＳＶ＝２０００００ｈ^−１の条件で流した時のＮＯ_ｘ 浄化率を測定した。結果を表３に示す。
【００５９】
【表３】

図１及び表３より、実施例１８の触媒は比較例７の触媒に比べて残留硫黄量が少ないにも関わらず、ＳＯ_２ の脱離量が多くなっている。すなわち実施例１８の触媒は、比較例７の触媒に比べて硫黄酸化物と反応しにくく、しかも反応して結合した硫黄分を脱離し易いことが明らかであり、硫黄被毒が著しく抑制されていることが明らかである。
【００６０】
一方、表３より、実施例１８〜２６の触媒は比較例７の触媒に比べて残留硫黄量が少なく、硫黄被毒が抑制されていることがわかる。またその結果、耐久試験後のＮＯ_ｘ 浄化率が向上していることも明らかである。
また実施例２０の触媒は他の実施例に比べてＮＯ_ｘ 浄化率が低いが、これはＷＯ_３／ＺｒＯ_２：Ａｌ_２Ｏ_３ 比が３：１であって全体の酸強度が特に高いこと、担体の比表面積が他より若干低いことから、ＮＯ_ｘ の吸蔵・還元能がある程度阻害されていると考えられる。
【００６１】
また実施例２５の触媒も他の実施例に比べてＮＯ_ｘ 浄化率が低いが、これはＷＯ_３／ＺｒＯ_２：Ａｌ_２Ｏ_３ 比が１：１４であって、ＷＯ_３／ＺｒＯ_２が少ないためにその作用が充分に発現しにくくなっていると考えられる。
【００６２】
【発明の効果】
すなわち本発明の排ガス浄化用触媒によれば、担体はきわめて高い酸性質を示すため、硫黄酸化物の近接が抑制され、また被毒を受けても容易に分解して硫黄分が速やかに脱離する。したがってＮＯ_ｘ 吸蔵体の硫黄被毒が著しく抑制されるので、高いＮＯ_ｘ 浄化能を有している。
【００６３】
そして高温耐久試験後においても、比較的低温域におけるＮＯ_ｘ 吸蔵体の硫黄被毒が抑制されるため、耐久試験後にも高いＮＯ_ｘ 吸蔵能が確保され、高いＮＯ_ｘ 浄化性能を維持することができる。
【図面の簡単な説明】
【図１】本発明の実施例１８の触媒と比較例７の触媒の、耐久試験後に昇温したときの温度と放出されたＳＯ_２ 量との関係を示すグラフである。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust gas purifying catalyst, and more particularly, to an exhaust gas containing an excessive amount of oxygen more than necessary to oxidize carbon monoxide (CO) and hydrocarbons (HC) contained in the exhaust gas. Nitrogen oxide (NO_xThe present invention relates to a catalyst capable of efficiently purifying the above.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, oxidation of CO and HC and NO_xA three-way catalyst is used for purifying exhaust gas by simultaneously performing reduction of the exhaust gas. As such a catalyst, for example, a catalyst in which a supporting layer made of γ-alumina is formed on a heat-resistant carrier such as cordierite and a noble metal such as Pt, Pd, and Rh is supported on the supporting layer is widely known. .
[0003]
By the way, the purification performance of such an exhaust gas purification catalyst greatly differs depending on the air-fuel ratio (A / F) of the engine. That is, on the lean side where the air-fuel ratio is large, that is, on the lean side where the fuel concentration is lean, the amount of oxygen in the exhaust gas increases, and the oxidation reaction for purifying CO and HC is active, but NO_xThe reduction reaction for purifying the catalyst becomes inactive. Conversely, on the rich side where the air-fuel ratio is small, that is, on the rich side where the fuel concentration is high, the amount of oxygen in the exhaust gas decreases, and the oxidation reaction becomes inactive but the reduction reaction becomes active.
[0004]
On the other hand, in running a car, acceleration and deceleration are frequently performed in the case of running in an urban area, and the air-fuel ratio frequently changes within a range from near stoichiometric (theoretical air-fuel ratio) to a rich state. In order to meet the demand for low fuel consumption in such traveling, it is necessary to operate on the lean side, which supplies an air-fuel mixture as much as possible. Therefore, NO on the lean side_xIt is desired to develop a catalyst that can sufficiently purify the catalyst.
[0005]
Therefore, the applicant of the present application has previously proposed an exhaust gas purifying catalyst in which an alkaline earth metal such as Ba and Pt are supported on a porous carrier such as alumina (for example, Japanese Patent Laid-Open No. 5-3176).52Gazette). Using this exhaust gas purifying catalyst, the air-fuel ratio is controlled in a pulsed manner from the lean side to the stoichiometric to rich side, so that NOx is occluded by the alkaline earth metal (NOx storage body) on the lean side. Since it is purified by reacting with reducing components such as HC and CO on the stoichiometric to rich side, NOx can be efficiently purified even in lean burn.
[0006]
However, in the exhaust gas, SO (S) contained in the fuel is combusted and produced.₂Which is oxidized by the catalytic metal in an oxygen-rich atmosphere to form SO 2₃It becomes. It is also easily converted to sulfuric acid by the water vapor contained in the exhaust gas, and these sulfur oxides are converted to NO such as alkaline earth metals._xReacts with the occlusion body to produce sulfites and sulfates,_xIt became clear that the occlusion body was poisoned and deteriorated. In addition, since a porous carrier such as alumina has a property of easily absorbing sulfur oxide, there is a problem that the above-mentioned sulfur poisoning is promoted.
[0007]
And like this NO_xWhen the occluder becomes sulfite or sulfate, NO_xCannot be occluded. As a result, in the above catalyst, NO_xThere was a problem that the purification performance of the fuel cell deteriorated.
In addition, titania has an acid property, and it is difficult to absorb sulfur oxide having an acid property. Therefore, an experiment was conducted in which the use of a titania carrier was recalled. As a result, SO₂Is not absorbed by titania, most of it flows downstream, and SO directly contacts precious metals.₂It has been clarified that the degree of poisoning is small because only is oxidized. However, a catalyst using a titania carrier has NO_xHas low initial purification performance._xIt has also been found that there is a fatal problem that the purification performance of the fuel cell remains low.
[0008]
Therefore, JP-A-8-99034 discloses that TiO₂-Al₂O₃, ZrO₂-Al₂O₃And #SiO₂-Al₂O₃At least one composite carrier selected from the group consisting of_xAn exhaust gas purifying catalyst supporting an occlusion body and a noble metal is disclosed.
According to this exhaust gas purifying catalyst, TiO₂, ZrO₂, SiO₂And Al₂O₃The advantages of each of_xHigh purification rate, NO absorption after endurance test because sulfur oxide absorption into carrier is suppressed_xThere is an advantage that the degree of reduction in the purification rate is small.
[0009]
JP-A-8-281116 discloses that a carrier made of zirconium phosphate contains NO._xAn exhaust gas purifying catalyst supporting an occlusion body and a noble metal is disclosed. According to this exhaust gas purifying catalyst, since zirconium phosphate is acidic, the approach of the sulfur oxide to the carrier is suppressed, and as a result, SO₂NO because oxidation of NO is suppressed_xSulfur poisoning of the occlusion body is suppressed.
[0010]
[Problems to be solved by the invention]
However, even in the exhaust gas purifying catalyst disclosed in the above publication, under severe conditions such as when the sulfur component in the fuel is large, the NO_xIt has been difficult to suppress sulfur poisoning of the steel.
Such a problem can be improved by further increasing the acidity of the carrier. However, in a conventional exhaust gas purifying catalyst, an acid-type carrier and NO_xDue to chemical bonding with the occlusion body or high crystallization, or in the case of a zirconium phosphate carrier, a phenomenon that the acid property of the carrier is reduced or disappears due to the deterioration of the surface, and the effect of suppressing sulfur poisoning gradually decreases. There was a problem of doing. Therefore, even if the acid property is increased, the acid property is significantly reduced or disappears after the high-temperature durability test._xIt becomes difficult to suppress sulfur poisoning of the occlusion body, and NO_xThere is a problem that purification ability is significantly reduced.
[0011]
The present invention has been made in view of such circumstances, and achieves both improvement of sulfur poisoning resistance in a relatively low temperature range and suppression of a decrease in the acidity of a carrier after a high-temperature durability test, thereby achieving a durability test. Later NO_xIt is intended to further improve the purification performance.
[0012]
[Means for Solving the Problems]
The feature of the exhaust gas purifying catalyst according to claim 1, which solves the above problem, is that:By controlling the air-fuel ratio from the lean side to the stoichiometric to rich side in a pulsed manner, NO _x A catalyst for purifyingWO_Three And MoO_ThreeAt least one ofTo 5 30 An acidic zirconia carrier composed of zirconia supported by weight%;At least one selected from the group consisting of alkali metals, alkaline earth metals and rare earth elementsAcid zirconia carrierNO supported on_x Occluder,Acidic zirconiaAnd a noble metal supported on a carrier.
[0013]
The feature of the exhaust gas purifying catalyst according to claim 2 is that:By controlling the air-fuel ratio from the lean side to the stoichiometric to rich side in a pulsed manner, NO _x A catalyst for purifying WO _Three as well as MoO _Three At least one of 5 30 A carrier composed of a mixture of an acidic zirconia carrier composed of zirconia supported by weight% and alumina, and at least one selected from alkali metals and alkaline earth metals supported on the carrier. NO _x An occlusion body, a noble metal supported on a carrier,Consists of
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
In the exhaust gas purifying catalyst according to claim 1 and claim 2,WO _Three as well as MoO _Three At least one of 5 30 Acidic zirconia carrier consisting of zirconia supported by weight%Is used. thisAcidic zirconiaThe support is presumed to have a coordination structure via an oxygen atom between a Zr atom and a W or Mo atom, but exhibits extremely strong acid properties. Also thisAcidic zirconiaThe carrier exhibits high stability even at high temperatures and maintains its acid properties.
[0015]
Therefore, in the exhaust gas purifying catalyst of the present invention, since the carrier maintains high acidity even after the high-temperature durability test, the adsorption of sulfur oxides on the carrier in a relatively low temperature range from the initial stage to after the high-temperature durability test in a lean atmosphere is suppressed. And no_x The reaction between the occluding body and the sulfur oxide is suppressed.
[0016]
furtherClaim 2Although the reason is unknown for the exhaust gas purifying catalyst described in_x It was also clarified that the reaction product between the storage material and the sulfur oxide was easily reduced. Therefore, sulfur poisoned NO_x Even if it is an occlusion body, SO_Two Easily desorbed NO_x The storage body is the original NO_x The storage capacity is easily restored.
Therefore, according to the exhaust gas purifying catalyst of the present invention, NO / NO_x NO is suppressed because sulfur poisoning of the occlusion body is suppressed._x NO from the initial stage to after the endurance test_x High NO with storage capacity_x Purification rate is ensured.
[0017]
Claim 1Used for the described catalystAcidic zirconiaThe carrier is WO_Three And MoO_ThreeComposed of at least one of zirconia andTo zirconiaWO_Three And MoO_ThreeAt least one of them is supported.
WO_Three And MoO_ThreeAt least one ofCarry amountIs 5 to 30% by weight in the carrier in total if both are contained.Range.If the amount is less than 5% by weight, the acidity of the carrier is not sufficient, and NO_x It becomes difficult to suppress the reaction between the occlusion body and the sulfur oxide, and the NO_x It becomes difficult to suppress a decrease in purification performance. Also WO_Three And MoO_ThreeAt least one ofCarry amountExceeds 30% by weight, although the acid properties are sufficient, the specific surface area decreases due to the reduction in the amount of zirconia._x The degree of decrease in occlusion capacity is significantly increased.
[0018]
The catalyst NO_x Considering the storage amount, WO_Three And MoO_ThreeAt least one ofCarry amountIs particularly preferably in the range of 5 to 25% by weight. NO if more than 25% by weight_x The storage amount will be low.
WO_Three And MoO_ThreeAt least one of the compounds is contacted with a solution of at least one compound of W and Mo with zirconia or zirconium hydroxide to support at least one compound of W and Mo on zirconia or zirconium hydroxide, and then calcined._Three And MoO_ThreeAt least one of zirconiaCan be carried.
[0019]
Claim 2The carrier used in the catalyst described in the,WO _Three as well as MoO _Three At least one of 5 30 Acidic zirconia carrier consisting of zirconia supported by weight%And alumina. The acidic zirconia carrier is a carrier used for the catalyst according to claim 1.Similarly, zirconiaWO_Three And MoO_ThreeAt least one ofIs the thing.
[0020]
Claim 2The carrier used in the catalyst described in the above, an acidic zirconia carrier and aluminaIt is a simple mixture.
Claim 2In the carrier used for the catalyst described in the above, the mixing ratio of the acidic zirconia carrier and alumina is desirably in the range of acidic zirconia carrier: alumina = 3: 1 to 1:14 by weight ratio. If the amount of the acidic zirconia support exceeds this range, it is considered that the overall acid strength becomes too high and the specific surface area becomes low._x The purification rate decreases. When the amount of the acidic zirconia support is less than this range, it is difficult to express the action of the acidic zirconia support, and NO after the durability test is performed._x Purification ability decreases.
[0021]
NO_xAs the occluding material, at least one selected from alkali metals, alkaline earth metals, and rare earth elements can be used. Examples of the alkali metal include lithium, sodium, potassium, rubidium, cesium, and francium. Further, the alkaline earth metal refers to an element of Group 2A of the periodic table, and examples thereof include barium, beryllium, magnesium, calcium, and strontium. Examples of the rare earth element include scandium, yttrium, lanthanum, cerium, praseodymium, and neodymium.
[0022]
NO_xThe content of the occluding material is preferably in the range of 0.05 to 1.0 mol per 120 g of the carrier. If the content is less than 0.05 mol, NO_xLow storage capacity and NO_xThe purifying performance is reduced, and even if the content exceeds 1.0 mol, the effect is saturated and a problem occurs due to a relative decrease in the amount of other components.
As the noble metal, one or more of Pt, Rh, and Pd can be used. In the case of Pt and Pd, the carrying amount is preferably 0.1 to 20.0 g, particularly preferably 0.5 to 10.0 g, per 120 g of the carrier. In the case of Rh, the amount is preferably from 0.01 to 80 g, particularly preferably from 0.05 to 5.0 g, per 120 g of the carrier. When converted to 1 liter of carrier volume, in the case of Pt and Pd, 0.1 to 20 g is preferable, and 0.5 to 10 g is particularly preferable. In the case of Rh, 0.01 to 10 g is preferable, and 0.05 to 5 g is particularly preferable.
[0023]
【Example】
Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.
(Example 1)
<Preparation of carrier>
Tungstic acid122.8 g of zirconium hydroxide was mixed with an aqueous solution obtained by dissolving 67.6 g of ammonium in 2.3 L of ion-exchanged water, stirred for 1 hour, and evaporated to dryness to remove the solvent. The obtained powder was further dried at 120 ° C., and calcined at 800 ° C. for 3 hours to obtain WO 2_Three/ ZrO_TwoA carrier powder was prepared.
<Support of precious metal>
WO obtained above_Three/ ZrO_TwoA predetermined amount of the carrier powder was impregnated with a predetermined amount of an aqueous solution of dinitrodiammine platinum, evaporated to dryness at 110 ° C., and calcined at 250 ° C. for 1 hour to carry 1.5% by weight of Pt.
<NO_x Carrying occlusion body>
WO loaded with Pt_Three/ ZrO_TwoThe carrier powder was impregnated with a predetermined amount of an aqueous potassium acetate solution, stirred for 1 hour, evaporated to dryness at 110 ° C., and calcined at 500 ° C. for 1 hour. The amount of K supported is WO_Three/ ZrO_TwoK is 0.3 mol per 120 g of carrier powder.
[0024]
This was compacted and then crushed to obtain a pellet catalyst of Example 1.
(Example 2)
Tungstic acidThe procedure of Example 1 was repeated, except that 116.3 g of zirconium hydroxide was mixed with an aqueous solution in which 135.1 g of ammonium was dissolved in 4.5 L of ion-exchanged water._Three/ ZrO_TwoA carrier powder was prepared. Then, Pt and K were carried in the same manner as in Example 1 to prepare a pellet catalyst of Example 2.
[0025]
(Example 3)
Tungstic acidIn the same manner as in Example 1 except that 103.4 g of zirconium hydroxide was mixed with an aqueous solution in which 270.2 g of ammonium was dissolved in 9.0 L of ion-exchanged water, WO_Three/ ZrO_TwoA carrier powder was prepared. Then, Pt and K were loaded in the same manner as in Example 1 to prepare a pellet catalyst of Example 3.
[0026]
(Example 4)
Tungstic acidIn the same manner as in Example 1 except that 71.1 g of zirconium hydroxide was mixed with an aqueous solution in which 270.2 g of ammonium was dissolved in 9.0 L of ion-exchanged water, WO_Three/ ZrO_TwoA carrier powder was prepared. Then, Pt and K were carried in the same manner as in Example 1 to prepare a pellet catalyst of Example 4.
[0027]
(Example 5)
Tungstic acidIn the same manner as in Example 1 except that 90.5 g of zirconium hydroxide was mixed with an aqueous solution in which 405.3 g of ammonium was dissolved in 8.1 L of ion-exchanged water, WO_Three/ ZrO_TwoA carrier powder was prepared. Then, Pt and K were carried in the same manner as in Example 1 to prepare a pellet catalyst of Example 5.
[0028]
(Example 6)
Tungstic acidIn the same manner as in Example 1 except that 103.4 g of zirconium hydroxide was mixed with an aqueous solution in which 270.2 g of ammonium was dissolved in 9.0 L of ion-exchanged water, WO_Three/ ZrO_TwoA carrier powder was prepared. Then, Pt was supported in the same manner as in Example 1, and Cs was supported in the same manner as in Example 1 except that cesium acetate was used instead of potassium acetate, whereby a pellet catalyst of Example 6 was prepared.
[0029]
(Example 7)
Tungstic acidIn the same manner as in Example 1 except that 103.4 g of zirconium hydroxide was mixed with an aqueous solution in which 270.2 g of ammonium was dissolved in 9.0 L of ion-exchanged water, WO_Three/ ZrO_TwoA carrier powder was prepared. Pt was supported in the same manner as in Example 1, and Ba was supported in the same manner as in Example 1 except that barium acetate was used instead of potassium acetate, to thereby prepare a pellet catalyst of Example 7.
[0030]
(Example 8)
Tungstic acidIn the same manner as in Example 1 except that 103.4 g of zirconium hydroxide was mixed with an aqueous solution in which 270.2 g of ammonium was dissolved in 9.0 L of ion-exchanged water, WO_Three/ ZrO_TwoA carrier powder was prepared. Then, Pt was supported in the same manner as in Example 1, and La was supported in the same manner as in Example 1 except that lanthanum acetate was used instead of potassium acetate, whereby a pellet catalyst of Example 8 was prepared.
[0031]
(Example 9)
An aqueous solution in which 5.6 g of molybdic acid was dissolved in 140.6 g of 1% aqueous ammonia was mixed with 122.8 g of zirconium hydroxide. After stirring for 1 hour, the solvent was removed by evaporation to dryness. The obtained powder was further dried at 120 ° C., and calcined at 800 ° C. for 3 hours to obtain MoO.₃/ ZrO₂A carrier powder was prepared.
<Support of precious metal>
MoO obtained above₃/ ZrO₂A predetermined amount of the carrier powder was impregnated with a predetermined amount of an aqueous solution of dinitrodiammine platinum, evaporated to dryness at 110 ° C., and calcined at 250 ° C. for 1 hour to carry 1.5% by weight of Pt.
<NO_xCarrying occlusion body>
MoO carrying Pt₃/ ZrO₂The carrier powder was impregnated with a predetermined amount of an aqueous potassium acetate solution, stirred for 1 hour, evaporated to dryness at 110 ° C., and calcined at 500 ° C. for 1 hour. The amount of K supported is MoO₃/ ZrO₂K is 0.3 mol per 120 g of the carrier powder.
[0032]
This was compacted and then crushed to obtain a pellet catalyst of Example 9.
(Example 10)
The same procedure as in Example 9 was conducted except that 116.3 g of zirconium hydroxide was mixed with an aqueous solution in which 11.3 g of molybdic acid was dissolved in 281.3 g of 1% aqueous ammonia.₃/ ZrO₂A carrier powder was prepared. Then, Pt and K were carried in the same manner as in Example 9 to prepare a pellet catalyst of Example 10.
[0033]
(Example 11)
MoO 2 was prepared in the same manner as in Example 9 except that 103.4 g of zirconium hydroxide was mixed with an aqueous solution in which 22.5 g of molybdic acid was dissolved in 562.6 g of 1% aqueous ammonia.₃/ ZrO₂A carrier powder was prepared. Then, Pt and K were loaded in the same manner as in Example 9 to prepare a pellet catalyst of Example 11.
[0034]
(Example 12)
In the same manner as in Example 9, except that 96.9 g of zirconium hydroxide was mixed with an aqueous solution in which 28.1 g of molybdic acid was dissolved in 703.2 g of 1% aqueous ammonia.₃/ ZrO₂A carrier powder was prepared. Pt and K were carried in the same manner as in Example 9 to prepare a pellet catalyst of Example 12.
[0035]
(Example 13)
In the same manner as in Example 9 except that 90.5 g of zirconium hydroxide was mixed with an aqueous solution in which 33.8 g of molybdic acid was dissolved in 843.8 g of 1% aqueous ammonia, MoO was used.₃/ ZrO₂A carrier powder was prepared. Then, Pt and K were loaded in the same manner as in Example 9 to prepare a pellet catalyst of Example 13.
[0036]
(Example 14)
The same procedure as in Example 9 was conducted except that 116.3 g of zirconium hydroxide was mixed with an aqueous solution in which 11.3 g of molybdic acid was dissolved in 281.3 g of 1% aqueous ammonia.₃/ ZrO₂A carrier powder was prepared. Then, Pt was supported in the same manner as in Example 9, and Cs was supported in the same manner as in Example 9 except that cesium acetate was used instead of potassium acetate, to thereby prepare a pellet catalyst of Example 14.
[0037]
(Example 15)
The same procedure as in Example 9 was conducted except that 116.3 g of zirconium hydroxide was mixed with an aqueous solution in which 11.3 g of molybdic acid was dissolved in 281.3 g of 1% aqueous ammonia.₃/ ZrO₂A carrier powder was prepared. Then, Pt was supported in the same manner as in Example 9, and Ba was supported in the same manner as in Example 9 except that barium acetate was used instead of potassium acetate, whereby a pellet catalyst of Example 15 was prepared.
[0038]
(Example 16)
The same procedure as in Example 9 was conducted except that 116.3 g of zirconium hydroxide was mixed with an aqueous solution in which 11.3 g of molybdic acid was dissolved in 281.3 g of 1% aqueous ammonia.₃/ ZrO₂A carrier powder was prepared. Then, Pt was supported in the same manner as in Example 9, and La was supported in the same manner as in Example 9 except that lanthanum acetate was used instead of potassium acetate, whereby a pellet catalyst of Example 16 was prepared.
[0039]
(Example 17)
WO obtained in Example 3₃/ ZrO₂A predetermined amount of the carrier powder was impregnated with a predetermined amount of an aqueous solution of dinitrodiammine platinum, evaporated to dryness at 110 ° C., and calcined at 250 ° C. for 1 hour to carry 1.5% by weight of Pt. Further, a predetermined amount of a rhodium chloride aqueous solution was impregnated, evaporated to dryness at 110 ° C., and calcined at 250 ° C. for 1 hour to carry 1.0% by weight of Rh.
[0040]
Then, Pt and K were carried in the same manner as in Example 1 to prepare a pellet catalyst of Example 17.
(Comparative Example 1)
Tungstic acidIn the same manner as in Example 1 except that 126.7 g of zirconium hydroxide was mixed with an aqueous solution in which 27.0 g of ammonium was dissolved in 1.0 L of ion-exchanged water, WO_Three/ ZrO_TwoA carrier powder was prepared. Then, Pt and K were carried in the same manner as in Example 1 to prepare a pellet catalyst of Comparative Example 1.
[0041]
(Comparative Example 2)
MoO was prepared in the same manner as in Example 9 except that 126.7 g of zirconium hydroxide was mixed with an aqueous solution in which 2.3 g of molybdic acid was dissolved in 56.3 g of 1% aqueous ammonia.₃/ ZrO₂A carrier powder was prepared. Then, Pt and K were carried in the same manner as in Example 9 to prepare a pellet catalyst of Comparative Example 2.
[0042]
(Comparative Example 3)
Using tetrapropoxytitanium and isopropylaluminum as starting materials, powders were prepared by a sol-gel method in such a ratio that Ti / Al = 1/8. The obtained powder is fired at 600 ° C. for 3 hours,₂-Al₂O₃This was a composite oxide carrier powder.
This TiO₂-Al₂O₃Pt and K were supported in the same manner as in Example 1 using the composite oxide carrier powder to prepare a pellet catalyst of Comparative Example 3.
[0043]
(Comparative Example 4)
Using tetrapropoxytitanium and isopropylaluminum as starting materials, powders were prepared by a sol-gel method in such a ratio that Ti / Al = 1/8. The obtained powder is fired at 600 ° C. for 3 hours,₂-Al₂O₃This was a composite oxide carrier powder.
This TiO₂-Al₂O₃After using the composite oxide carrier powder and supporting Pt as in Example 1, Ba was supported as in Example 1 except that barium acetate was used instead of potassium acetate, and A pellet catalyst was prepared.
[0044]
(Comparative Example 5)
TiO₂Powder and γ-Al₂O₃The powder is mixed at a ratio of 1/4 by weight,₂/ Al₂O₃A carrier powder was prepared. This TiO₂/ Al₂O₃Using the carrier powder, after supporting Pt in the same manner as in Example 1, Ba was supported in the same manner as in Example 1 except that barium acetate was used instead of potassium acetate, and the pellet catalyst of Comparative Example 5 was used. Prepared.
[0045]
(Comparative Example 6)
Phosphoric acid was added to zirconium chloride to produce zirconium phosphate hydrate, and calcined at 900 ° C. for 5 hours to prepare a zirconium phosphate carrier powder.
Using this zirconium phosphate carrier powder, Pt and K were carried in the same manner as in Example 1 to prepare a pellet catalyst of Comparative Example 6.
[0046]
<Evaluation test>
For each of the above pellet catalysts, a model gas D shown in Table 1 was used at a temperature of 300 ° C. and a space velocity SV = 200000 h.^-1NO stored for 10 minutes per gram of catalyst when flowing under the conditions_xThe amount was measured. Table 2 shows the results.
On the other hand, a heat treatment was performed by flowing a model gas A (stoichiometric) shown in Table 1 at 900 ° C. for 5 hours. Subsequently, heat treatment was performed at 400 ° C. for 20 minutes while alternately flowing model gas B (rich) and model gas C (lean) alternately for 1 minute and 4 minutes, respectively.
[0047]
Then, for each of the pellet catalysts after the heat treatment, the model gas D was used, the input gas temperature was 300 ° C., and the space velocity SV was 200000 h.^-1NO stored for 10 minutes per gram of catalyst when flowing under the conditions_xThe amount was measured. Table 2 shows the results.
Also the initial NO_xStorage amount and NO after heat treatment_xCalculate the difference between the occlusion amounts and calculate the initial NO of the difference._xThe ratio (change rate) to the occlusion amount was calculated, and the results are shown in Table 2.
[0048]
[Table 1]

[0049]
[Table 2]

[0050]
Table 2 shows that the catalysts of the examples had a small change rate of less than 50%, and that NO_xWhile the degree of decrease in the occlusion ability is small, the change rate of the catalyst of the comparative example is as large as 69% or more._xThe storage capacity has dropped significantly. That is, the catalyst of the example was NO compared to the catalyst of the comparative example even after the heat treatment._xIt is clear that the sulfur poisoning of the occlusion body is suppressed.
[0051]
Further, when comparing the examples, WO₃Or MoO₃The catalysts of Example 5 and Example 13 in which the amount of_xSince the absolute amount of storage is small, WO₃Or MoO₃It is also clear that it is particularly desirable that the content be 25% by weight or less.
As described above, it is not clear why the catalyst of the example suppresses sulfur poisoning even after the heat treatment as compared with the comparative example, but the catalyst of the example has a higher acidity than the catalyst of the comparative example due to the high-temperature heat treatment. It is considered that the degree of decrease is small and the heat resistance of the carrier is high.
[0052]
(Example 18)
20.3 g of ammonium tungstate was dissolved in an aqueous solution of oxalic acid, and 110.0 g of zirconium hydroxide was mixed therein and stirred for 1 hour, and then water was removed by evaporation to dryness. Subsequently, it was dried in a drying oven at 120 ° C. and fired in the air at 800 ° C. for 3 hours.
WO obtained₃/ ZrO₂Γ-Al powder₂O₃The powder was mixed with the powder at a weight ratio of 1: 1. The mixed powder was impregnated with a predetermined amount of a dinitrodiammine platinum aqueous solution having a predetermined concentration, and calcined at 250 ° C. for 1 hour in the atmosphere. Further, a predetermined amount of an aqueous solution of potassium acetate having a predetermined concentration was impregnated, evaporated to dryness, and calcined at 500 ° C. for 1 hour in the air to obtain a catalyst powder of Example 18. The supported amount of Pt is 1% by weight, and the supported amount of K is 6% by weight.
[0053]
(Example 19)
After supporting Pt on the mixed powder obtained in the same manner as in Example 18, a predetermined amount of an aqueous solution of potassium acetate having a predetermined concentration was impregnated, evaporated to dryness, and then calcined at 250 ° C. for 1 hour in the atmosphere. This powder was further impregnated with a predetermined amount of a barium acetate aqueous solution having a predetermined concentration, evaporated to dryness, and calcined at 500 ° C. for 1 hour in the air to prepare a catalyst powder of Example 19. The supported amount of Pt is 1% by weight, the supported amount of K is 3% by weight, and the supported amount of Ba is 9% by weight.
[0054]
(Examples 20 to 25)
WO obtained in the same manner as in Example 18₃/ ZrO₂Powder and γ-Al₂O₃Except that the mixing ratio with the powder was changed as shown in Table 3, the same procedure as in Example 18 was carried out to prepare the catalyst powder of each example. The supported amount of Pt in each catalyst powder was 1% by weight, and the supported amount of K was 6% by weight.
[0055]
(Example 26)
Molybdic acid (13.0 g) was dissolved in oxalic acid aqueous solution, and zirconium hydroxide (141.2 g) was mixed therein and stirred for 1 hour, and then water was removed by evaporation to dryness. Subsequently, it was dried in a drying oven at 120 ° C. and fired in the air at 800 ° C. for 3 hours.
MoO obtained₃/ ZrO₂Γ-Al powder₂O₃The powder was mixed with the powder at a weight ratio of 1: 1. The mixed powder was impregnated with a predetermined amount of a dinitrodiammine platinum aqueous solution having a predetermined concentration, and calcined at 250 ° C. for 1 hour in the atmosphere. Further, a predetermined amount of a potassium acetate aqueous solution having a predetermined concentration was impregnated, evaporated to dryness, and calcined at 500 ° C. for 1 hour in the air to obtain a catalyst powder of Example 26. The supported amount of Pt is 1% by weight, and the supported amount of K is 6% by weight.
[0056]
(Comparative Example 7)
TiO₂Γ-Al powder₂O₃The powder was mixed with the powder at a weight ratio of 1: 1. The mixed powder was impregnated with a predetermined amount of a dinitrodiammine platinum aqueous solution having a predetermined concentration, and calcined at 250 ° C. for 1 hour in the atmosphere. Further, a predetermined amount of a potassium acetate aqueous solution having a predetermined concentration was impregnated, evaporated to dryness, and calcined at 500 ° C. for 1 hour in the air to obtain a catalyst powder of Comparative Example 7. The supported amount of Pt is 1% by weight, and the supported amount of K is 6% by weight.
[0057]
(Test / Evaluation)
Each of the catalyst powders was granulated into pellets of 1.0 to 1.7 mm to obtain respective pellet catalysts. Each of the pellet catalysts was placed in an evaluation device, and a rich model gas (model gas B in Table 1) corresponding to A / F = 12 and a lean model gas (model gas C in Table 1) corresponding to A / F = 21 were used. ) Was switched at a time of 1 minute / 4 minutes, and an endurance test was conducted in which the gas was supplied at 700 ° C. for 5 hours.
[0058]
The catalyst powders of Example 18 and Comparative Example 7 after the endurance test were heated from room temperature to 700 ° C. at a rate of ° C./min.₂Was measured. The results are shown in FIG.
In addition, the residual amount of sulfur was measured for each of the pellet catalysts after the durability test, and using the model gas D shown in Table 1, the inlet gas temperature was 300 ° C., and the space velocity SV was 200000 h.^-1NO when flowing under the conditions of_xThe purification rate was measured. Table 3 shows the results.
[0059]
[Table 3]

From FIG. 1 and Table 3, it can be seen that the catalyst of Example 18 had a lower SO₂Is increasing. That is, it is clear that the catalyst of Example 18 is less likely to react with sulfur oxides than the catalyst of Comparative Example 7, and it is easy to desorb the sulfur component which has reacted and bonded, and sulfur poisoning is significantly suppressed. It is clear that there is.
[0060]
On the other hand, from Table 3, it can be seen that the catalysts of Examples 18 to 26 have a smaller residual sulfur amount than the catalyst of Comparative Example 7, and the sulfur poisoning is suppressed. As a result, the NO after the endurance test_xIt is also clear that the purification rate is improving.
Further, the catalyst of Example 20 is NO_xPurification rate is low, but this is WO₃/ ZrO₂: Al₂O₃Since the ratio is 3: 1 and the overall acid strength is particularly high, and the specific surface area of the carrier is slightly lower than the others, NO_xIt is considered that the occlusion / reduction ability of the phenol is inhibited to some extent.
[0061]
Further, the catalyst of Example 25 was also NO compared with the other examples._xPurification rate is low, but this is WO₃/ ZrO₂: Al₂O₃The ratio is 1:14 and WO₃/ ZrO₂It is considered that the effect is less likely to be sufficiently exhibited due to the small amount.
[0062]
【The invention's effect】
That is, according to the exhaust gas purifying catalyst of the present invention, since the carrier exhibits extremely high acidity, the proximity of sulfur oxides is suppressed, and even if it is poisoned, it is easily decomposed and the sulfur content is quickly desorbed. I do. Therefore NO_xSince the sulfur poisoning of the occlusion body is significantly suppressed, high NO_xHas purification ability.
[0063]
Even after the high-temperature endurance test, NO_xSince sulfur poisoning of the occlusion body is suppressed, high NO_xHigh storage NO with high storage capacity_xPurification performance can be maintained.
[Brief description of the drawings]
FIG. 1 shows the temperature of the catalyst of Example 18 of the present invention and the catalyst of Comparative Example 7 when the temperature was increased after an endurance test and the released SO.₂It is a graph which shows the relationship with quantity.

Claims (2)

NO _x in the exhaust gas by controlling such that the stoichiometric-rich side air-fuel ratio from the lean side to the pulse-like A catalyst for purifying
An acidic zirconia carrier comprising zirconia supporting 5 to 30 % by weight of at least one of WO ₃ and MoO ₃ ;
Alkali metal, and _the NO _x storage material carried on the acidic zirconia support at least consists one selected from alkali earth metals and rare earth elements,
Exhaust gas purifying catalyst, characterized a noble metal supported on the acidic zirconia support, in that it consists of. By controlling the air-fuel ratio from the lean side to the stoichiometric to rich side in a pulsed manner, NO _x A catalyst for purifying
WO _Three as well as MoO _Three At least one of 5 30 A carrier consisting of a mixture of an acidic zirconia carrier comprising alumina and zirconia supported by weight%;
  Consisting of at least one selected from alkali metals and alkaline earth metals, supported on the carrier NO _x Occluder,
  An exhaust gas purifying catalyst, comprising: a noble metal supported on the carrier.

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